hosts/nullbox/btrfs-clean.nix

@@ -1,108 +0,0 @@
-{ config, lib, utils, pkgs, ... }:
-let
-  inherit (lib) escapeShellArg optionalString concatStringsSep
-    nameValuePair mapAttrs' filterAttrs mapAttrsToList
-    mkIf mkOption types;
-  inherit (utils) escapeSystemdPath;
-  # (wip) more configurable than old one, will be used by volatile btrfs module
-
-  genBtrfsInit' = fsConfig: genBtrfsInit {
-    inherit (fsConfig) device;
-    inherit (fsConfig.btrfs) subvolume;
-    inherit (fsConfig.btrfs.cleanOnBoot) destination;
-  };
-  genBtrfsInit = { subvolume, device, destination, }:
-  ''
-    mkdir -p /btrfs_tmp
-    mount ${escapeShellArg device} /btrfs_tmp -o subvol=/
-
-    # ensure subvol parent directory exists
-    mkdir -p $(dirname /btrfs_tmp/${escapeShellArg subvolume})
-
-    if [[ -e /btrfs_tmp/${escapeShellArg subvolume} ]] ; then
-      mkdir -p /btrfs_tmp/${escapeShellArg destination}
-      timestamp=$(date --date="@$(stat -c %Y /btrfs_tmp/${escapeShellArg subvolume})" "+%Y-%m-%-d_%H:%M:%S")
-      mv /btrfs_tmp/${escapeShellArg subvolume} /btrfs_tmp/${escapeShellArg destination}/"$timestamp"
-    fi
-
-    btrfs subvolume create /btrfs_tmp/${escapeShellArg subvolume}
-
-    umount /btrfs_tmp
-
-  '';
-    # TODO implement deletion once system is booted. the old implementation did
-    # it here, which is not safe until system time is at least monotonic.
-    # systemd tmpfiles is good enough, just mount it to somewhere in /run
-
-  generateInitrdUnit = name: values: let
-    deviceUnit = "${escapeSystemdPath values.device}.device";
-  in nameValuePair "btrfs-clean-subvolume-${escapeSystemdPath name}" {
-    description = "BTRFS subvolume reset for ${name} mountpoint";
-    wantedBy = [ "initrd-root-fs.target" ];
-    before = [ "sysroot.mount" ];
-    after = [ deviceUnit ];
-    requires = [ deviceUnit ];
-    serviceConfig = {
-      Type = "oneshot";
-      RemainAfterExit = true;
-      Exec = pkgs.writeShellScript "btrfs-clean-subvolume" (genBtrfsInit' values);
-    };
-  };
-
-  fsModule = { config, name, ... }:
-  {
-    options.btrfs = {
-      subvolume = mkOption {
-        description = "btrfs subvolume of filesystem";
-        type = with types; nullOr path;
-        default = null;
-      };
-      cleanOnBoot = {
-        enable = mkOption {
-          description = ''
-            Whether to replace this subvolume with an empty one before mount.
-            This is useful in combination with Impermanence.
-          '';
-          type = types.bool;
-          default = false;
-          example = true;
-        };
-        destination = mkOption {
-          description = ''
-            Destination of old subvolume, relative to btrfs root (subvol=/).
-            Cleanup is handled as a separate step, in case any old state is
-            needed.
-          '';
-          type = types.path;
-          example = "/old_roots";
-        };
-      };
-    };
-    config = {
-      options = let
-        inherit (config.btrfs) subvolume;
-      in lib.mkIf (!(isNull subvolume)) [ "subvol=${subvolume}" ];
-    };
-  };
-in
-{
-  options = {
-    fileSystems = mkOption {
-      type = with types; attrsOf (submodule fsModule);
-    };
-  };
-  config = let
-    configuredFileSystems = filterAttrs (k: v: v.btrfs.cleanOnBoot.enable) config.fileSystems;
-  in mkIf (configuredFileSystems != { }) {
-
-    assertions = mapAttrsToList (name: values:
-      { assertion = (!(isNull values.btrfs.subvolume));
-        message = "`fileSystems.${name}.btrfs.cleanOnBoot.enabled` is set to true, but `filesystems.${name}.btrfs.subvolume` is not set."; }) configuredFileSystems;
-
-    boot.initrd.systemd.services = mapAttrs' generateInitrdUnit configuredFileSystems;
-
-    boot.initrd.postDeviceCommands = let
-      scripts = mapAttrsToList (name: values: genBtrfsInit' values) configuredFileSystems;
-    in mkIf (!config.boot.initrd.systemd.enable) (lib.mkAfter (concatStringsSep "\n" scripts));
-  };
-}

hosts/nullbox/impermanence.nix

@@ -29,9 +29,6 @@ let
 
   root_vol = "/dev/archdesktop/root";
 in {
-  imports = [
-    ./btrfs-clean.nix
-  ];
   config = lib.mkIf (!(config.virtualisation ? qemu)) {
     fileSystems."/persist" = {
       neededForBoot = true;
@@ -40,16 +37,17 @@ in {
       options = [ "subvol=/nixos/@persist" ];
     };
 
+    # TODO volatile btrfs module
+    boot.initrd.postDeviceCommands = lib.mkAfter (mkBtrfsInit {
+      volume = root_vol;
+      volatileRoot = "/nixos/volatile";
+      oldRoots = "/nixos/old_roots";
+    });
+
     fileSystems."/" = lib.mkForce {
       device = root_vol;
       fsType = "btrfs";
-      btrfs = {
+      options = [ "subvol=/nixos/volatile" ];
-        subvolume = "/nixos/volatile";
-        cleanOnBoot = {
-          enable = true;
-          destination = "/nixos/old_roots";
-        };
-      };
     };
     environment.persistence = {
       "/persist/nobackup" = {